The neuropeptides somatostatin and galanin are present in the iris and may modulate pupil diameter. We examined the effects of somatostatin and galanin on isolated rabbit iris dilator and sphincter smooth muscles that were mounted in an organ bath. An isometric transducer recorded changes in tension in response to electric field stimulation (100 Hz, 0.3 msec in duration, 10 V in strength) delivered by a pair of platinum plate electrodes. The dilator muscle response to field stimulation was not… CONTINUE READING